Enable Gitter notifications on CI builds.

.travis.yml

@@ -3,6 +3,14 @@ language: java
 jdk:
   - oraclejdk8
 
+notifications:
+  webhooks:
+    urls:
+      - https://webhooks.gitter.im/e/5e9ccd41111917b19478
+    on_success: change  # options: [always|never|change] default: always
+    on_failure: always  # options: [always|never|change] default: always
+    on_start: never     # options: [always|never|change] default: always
+
 # http://docs.travis-ci.com/user/migrating-from-legacy
 sudo: false
 cache: bundler